Control apparatus



A ril 13, 1943. -r. R. HARRISON 2,316,240

CONTROL APPARATUS Filed Oct. 51, 1941 s She ets-Shee. 1

5 lu l? v, FIGJ.

AI l 2 9 l, V M F0 INVENTOR THOMAS R. HARRISON April 13, 1943. T. R.HARRISON 2,316,240

CONTROL APPARATUS 3 Sheets-Sheet 2 Filed Oct. 51, 1941 INVENTOR' THOMASR. HARRISON A ORNEY April 13, 1943. I T. R. HARRISON 2,316,240

CONTROL APPARATUS Filed Oct. 31, 1941 3 Sheets-Sheet 3 I 8 v \NVENTOR vTHOMAS R. HARRKSON AT ORNEY Patented-Apr. 13, 1943 UNITED STATES PATENTOFFICE CONTRQL APPARATUS Thomas R. Harrison, Wyncote, Pa., assignor to v.The Brown-Instrument Company, Philadelphia, Pa, a corporation ofPennsylvania Application October 31, 1941, Serial No. 417,303

19 Claims. (01. 17195)' The present invention relates to controlapparatus and more particularly to electrical control apparatusembodying means, auxiliary to the basic apparatus needed to control avariable con-.- dition, to anticipate the need for a correction be- I toprovide such control apparatus wherein the auxiliary means comprisesuitably connected electrical resistance andreactance means which areadapted to displace the control point of the condition being controlledthrough a small rrnge and in a sense to meet the changing trend of hecondition and thus effect a corrective adjustment before the truecontrol point is reached following parture in the working zonetemperature from the desired value, the lag referred to in the transferof heat from the heating zone to the working zone tends to permit anundesired magnified variation in the supply of agent to the heating zoneand, as a result, overshooting and consequent hunting of the workingzone temperature about the control point. This effect is produced eventhough the supply of heat producing agent is cut off at the instant theworking zone temperature reaches the control point because the energystored in the heating zone will continue for some time after the supplyof heat producing a departure of said condition from said true controlpoint. a

Still another object of the present invention is to provide controlapparatus adapted to effect such operation in a manner to avoid drift ofn the control point, which, for example, tends to be produced by changesin load in a furnace.

Another specific object of the present invention is to provide suchcontrol apparatus wherequantity. The reguiation'of the temperature in afurnace is an example of a control application in which such a conditionis encountered. Because of structural requirements in furnaces there isusually a zone where the heat is applied and a separate and physicallydisplacedzone where the work to be treated is placed. As a .result ofsuch physical displacement of the heating and working zones in thefurnace, a lag or agent is cut off to supply theheat to raise thetemperature of the working zone.

Various methods and apparatus arrangements have been employed in theprior art to reduce the extent and duration of departure of the workingzone temperature from the desired value. For example. it has beenproposed to control the temperature of the working zone by controllingthe application of fuel to the heating zone in accordance with thetemperature of the heating zone. I It has also been proposed to controlthe temperature of the working zone by controlling the application ofheat in accordance with the difference in temperature between theheating zone and the working zone. Such methods have notprovensatisfactory, however, because the temperature in the working zoneis dependent in part upon the thermal condition and capacity of theworking zone, which factors in turn vary in accordance with thecharacter of the work under treatment and the conditions of use are notconstant factors but instead are variable and impredictable,unpredictable at least with any ture has passed the desired controlpoint wherethat heat to the working zone.- Sinceit is ordisupply of heatproducing agent to the heating zone is controlled thereby. Such controlprovisions leave much to be desired from the standpoint of good control,however, in that on a de- ,by overshooting and hunting are avoided. In aspecific embodiment of the invention a controlling pyrometer forregulating the operation of a fuel supply valve is operated in responseto a current flow in a measuring circuit produced by a thermocouplewhich is subjected to the temperature it is desired to constantlymaintain at a'predeterznined value. Also included in said measuringcircuit are resistance and reactance means which operate to modify theeffect on the controlling pyrometer of any changes in saidthermoelectric eurrentas required to effect a c0rrective adjustment ofthe fuel supply valve be- [ore the temperature has reached saidpredetermined value, that is, in anticipation of a need for suchcorrective adjustment.

The various features of novelty which characterize my invention arepointed out with particularity in the claims annexed to and forming partof this specification. For a better understanding of the invention,however, its advantages andspeciflc objects obtained with its use,reference should be had to the accompanying drawings and descriptivematter in which I have illustrated preferred embodiments of theinvention. I

Of the drawings:

Fig. 1 is a control network diagram illustrating the use of my inventionin a simple millivoltmeter control system utilizing a galvanometer;

Fig. 2 is a view similar to Fig. 1 illustrating an alternativearrangement for obtaining the desired anticipating action;

Fig. 3 is a further modification of the Fig. l. arrangement illustratingthe use of my invention in a deflectional type potentiometer system;

Figs. 4 and 5 are different modifications illus trating the use of myinvention in proportioning type control systems including resetprovisions; and

Figs. 6 and 7 illustrate an alternative arrangement for effecting thedesired control operations in response to the deflections of thegalvanometer.

The embodiment of my invention illustrated more or less diagrammaticallyin Fig. 1 comprises an electrical regulating device which is adapted toeffect so-called floating control regulating pointer 2 is in engagementwith the contact II the rotor will rotate in the opposite direction.

,Rotor I5 is connected through suitable gearing operation and utilizes ameasuring circuit of the simple millivoltmeter class. The regulatingdevice includes a galvanometer I having a needle or pointer 2 which isadapted to be deflected in response to the variations in temperaturewithin the work chamber of a furnace 3 as measured by a thermocouple lwhichis inserted in the work chamber and is connected by conductingleads 5 and 6 to the terminals of the galvanometer i. As shown, acapacitance I having a resistance I connected in shunt therewith isincluded in the con ductor 5. The function of the capacitance l andresistance 8 in the control device is explained in detail hereinafter.

The deflecting element or pointer 2 of galvanometer I is disposed inoperative relation with a pair of stationary contacts I and III whichare positioned on opposite sides of it and slightly displaced therefromThe contacts 9 and III are connected to one end of a respective windingII and I2 of a two-phase reversible electrical motor I3, the other endsof which are connected together and to the conductor L of an alternatingcurrent supply source. The other conductor 1: of the supply source isconnected to the salvanometer pointer 2' through a flexible connectionas shown. A condenser I4 is connected between the contacts 8 and HI andis provided to effect a phase shift of approximately 90 in thealternating current flow through one motor winding H or l2 with respectto that in the other winding when the pointer 2 is in engagement withone or the other of the contacts l0 or 8, respec-.

or other means to the operating stem of a valve 16 which is inserted ina fuel supply pipe I! leading to the heating region of the furnace l,and is adapted to vary the degree of opening of the valve and therebythe. flow of fuel to the furnace.

As in the usual millivoltmeter controller, the current generated by thethermocouple 4 produces a deflection of the pointer 2 of thegalvanometer against the opposing action of suitable spring means (notshown) within the galvanometer. When the current generated by thethermocuple' falls below a value corresponding to the temperature forwhich the apparatus is preadjusted and at which the pointer 2 is out ofengagement with both of the contacts 9 and III, the pointer 2 deflectsinto engagement with the contact l0 and energizes the motor for rotationin the direction to effect an opening adjustment of the fuel supplyvalve l6 and thereby an increase in the supply of fuel to the furnaceheating chamber. As the heat in theheating chamber is graduallytransferred to the working chamber, the current generated by thethermocouple is increased and eventually that current is built up to apoint at which the pointer 2 moves out of engagement with the contactl0. Limit switches (not shown) may desirably be provided in the motorenergizing circuit to deenergize the motor in the event the fuel valve18 is adjusted to one or the other of its extreme positions before thefurnace working temperature has been returned to the desired value.Similarly, on an increase in temperature in the work chamber, thepointer 2 will deflect into engagement with the contact 9 and effect aclosing adjustment of the valve ll to-return the work chambertemperature to the desired value.

i Thus far, the operation of the arrangement of Fig. i has beendescribed without reference to I the novel auxiliary control provisionsincluding tively. The effect of such shift in phase of the direction.Thus, when the galvanometer pointer 2 is in engagement with the contactI, the rotor I5 will rotate in one direction and when the condenser Iand resistance 8 referred to hereinbefore. The tendency of theseauxiliary control provisions is to temporarily modify the currentsupplied to the galvanometer from the thermocouple in response to anychange in the working temperature of the furnace to simulate a conditiondifferent from that which actually exists in the work chamber upondeparture of the working temperature from the desired value to the endthat initially a large valve correction is produced, and in addition, avalve correction is produced in anticipation of the need for suchcorrection.

Speciflcally, with the control apparatus stabilized and the workingtemperature of the furnace at the normal, desired value, theelectromotive force developed by the thermocouple 4 will be dividedbetween the galvanometer l and the parallel connected condenser 1 andresistance 8 in proportion to the relative resistances of the elements Iand 8. In the case considered the component of electromotive forceacross the galvanometer I will be precisely that required to maintainthe galvanometer pointer 2 out of engagement with the contacts 9 and II,and as a result the motor It will be stationary with the fuel valve l6adjusted to some position intermediate its limits of adjustment.

On a sudden departure of the temperature of the furnace work chamberfrom the desired control point, for example, on an increase in workchamber temperature, the electromotive force ,the only effect ofcondenser to restore the furnace work temperature to the generated bythe thermocouple 4 will increase to acorresponding extent. This increasein electromotive force is not immediately divided between the resistance8 and the galvanometer however,

but instead the full change is momentarily applied to the galvanometer Ibecause of the action of the capacitance 1 which tends to prevent anysudden changes in the potential across its terminals. The resultingdeflection of the galvanometer pointer 2 into engagement with thecontact 9 energizes the motor 3 for operation in the direction todecrease the supply of fuel to the furnace heating chamber as explainedhereinbefore.

The capacitance I does not continue to hold its previous charge tomaintain the potential across the resistance 8 at its original value,however, but gradually charges until the el'ectromotive force developedby the thermocouple 4 is divided between the resistance 8 andgalvanometer l in proportion to the relative resistances of theseelements. With no further change in the furnace this end the condenserwork temperature the potentials across the condenser T and galvanometerI will then be of greater magnitude by an amount corresponding to theextent of the temperature change'than they were prior to the temperaturechange. Up to this point, therefore, the action of the control system isno different than it would be if the condenser and resistance 8 were notemployed, 1 and resistance 8 having been either to cause beyond contact9 or to cause contact between-pointer the time the charge denser 1.

greater pressure of pointer 2 to travel 2 and contact 9 during waschanging on com.

' When subsequently the furnace temperature begins to return toward thedesired value, the electromotive force developed by the thermocouple 4will begin to decrease to its original value. This decrease inelectromotive force, as in the case of the increase of electromotiveforce considered above, is not immediately divided between theresistance 8 and the galvanometer I, but is first assumed in itsentirety by the galvanometer I because of the tendency of the condenserto resist any change iii-potential across its terminals. The effect ofthis action is that the deflection of the galvanometer pointer 2 awayfrom contact 9 and possibly on to contact in, in

response to the temperature change, is accelerdesired value isanticipated, and as a result, the furnace work temperature is quicklyrestored-to the desired value.

Such anticipation in the corrective adjustment of valve It will beeffected upon a decrease in furnace work temperature following asustained condition of the furnace work temperature at the desired valuein a manner similar to that just described for a furnace worktemperature increase.

It will be readily apparent, therefore, that by properly proportioningcondenser 'l and resistor 8, the use of the auxiliary control provisionsdescribed will operate to reduce the departures from normal temperature,both in magnitude and frequency, and accordingly, more uniform workingconditions will be maintained in the furnace. To 1 and resistance 8 aremade adjustable in magnitude. As shown, the resistance 8 may be providedwith a knob 8a which may be manipulated to vary the resistance.

As will be understood by those skilled in the art, the control point, ormother words the temperature it is desired to maintain in the furnace 7of Fig. 1, in which modification an inductive rey mas l9 actance andassociated resistance have been substituted for the capacitive reactance1 and resistance '8 of Fig. l. The said inductive reactance comprises atransformer |8 having a primary winding l9 and a secondary winding 20connected in series relation and inserted in the conductor 5. 'I'heassociated resistance referred to, and designated by the referencenumeral 2| is connected between the point of engagement of windand 20and the conductor 6. The resistance of the transformer windings I9 and20 is ated. That is to say, prior to the time when the electromotiveforce of the thermocouple 4 has decreased to the value corresponding tothe desired furnace work temperature, the potential applied togalvanometer l will'have been reduced to a value less than that requiredto maintain the pointer 2 in engagement with the contact 9 and mayevendecrease to such an extent that the pointer 2 will deflect intoenagement with the contact I0. In the first case the motor |3 will bedeenergized and thereby the adjustment of valve l6 stopped prior to thetime the furnace work chamber temperature is returned to the desiredvalue. In the second case,

namely, the case when the pointer 2 is deflected into engagement withthe contact I0, an energizing circuit will be closed to the motor I?!for effecting an opening adjustment of the fuel In both cases thenegligible compared to the resistance of the resistance 2| With thismodified arrangement, when the furnace work temperature has beenstabilized at the desired normal value for a considerable time. thepotential applied to the terminals of the gal vanometer I will beprecisely that required to maintain the pointer 2 intermediate thecontacts 9 and I0 and out of engagement with both of said-contacts. Itis noted that thiselectromotive force is substantially equal in magnitudto the potential drop maintained across the resistance 2| by the flow ofthermocouple current.

This is the case because the resistance of the transformer windings l9and 20 is practically negligible compared to the resistance ofresistance 2|, and because the current flow through the primary winding9 is then-steady in value whereby the electromotive force induced in thesecondary winding 28 is substantially zero in value.

On a departure in the furnace work chamber temperature from the desiredvalue the electromotive force developed by thermocouple 4 will changeaccordingly to change in current flow through the resistance 2| producea. correspondingin the transformer secondary winding 20 which isadditive to that produced across the resistance 2|. The potentialapplied-to the terminals of galvanometer I will thus be increased firstby the increase in the potential drop produced across resistance 2|directlyby the change in thermocouple current, and second by thecomponent of electromotive force induced in the transformer secondarywinding 20 as a result of the change in thermocouple current through thetransformer primary winding I9. The consequent deflection ofgalvanometer pointer 2 into engagement with contact 9 energizes themotor III for rotation in the direction to decrease the supply of fuelto the furnace heating chamber.

The effect of th last mentioned component of electromotive force is toaccentuate'the deilection of the galvanometer pointer 2 in response to afurnace temperature change, that is, to maintain the galvanometerpointer 2 in engagement with contact 9 for a longer period than it wouldbe maintained if the transformer H! were dispensed with, and thereby toaccentuate the correction of fuel valve |8 which is produced.

The component of electromotive impressed on th galvanometer by thetransformer l8 does not continue indefinitely, however, but graduallydiminishes in value if there is no further change in the electromotiveforce produced by thermocouple 4. With no further change in the furnacework chamber, therefore, the potential impressed on the galvanometer Iwill then correspond to the potential drop across resistance 2| and willbe of greater magnitude b an amount corresponding to the extent of thetemperature change than it was prior to the temperature change.

As the furnace work chamber temperaturegradually returns to the desiredvalue, the electromotive force developed by the thermocouple 4 willbegin to decrease to its original value and the change in current flowthrough transformer primary winding |9 will cause the induction of anelectromotive force in the secondary winding 20 which is opposed to thatproduced across the resistance 2|. The potential impressed on theterminals of th galvanometer will, therefore be decreased in the firstplace by the decrease in the-potential drop across resistance 2| causedby the reduced thermocouple electromotive force, and in the second placeby the component of electromotive force induced in the. transformer plyvalve l8 before the furnace work temperature has reached the controlpoint. That is to say, a correction in the supply of heating agent tothe furnace is made in anticipation of the need for such correction inmuch the same manner as adjustment is made in the supply of heatingagent to the furnace by means of the Fig. 1

arrangement utilizing a capacitive reactance in the conductor 5 insteadof inductive reactance.

Such anticipation inthe corrective adjustment of valve ||i will be madein a manner similar to that Just described upon a decrease in thefurnace work temperature from the desired value following a condition ofstabilization at the desired value also. Accordingly, by properlydesigning transformer I8 and resistance 2| the use of the auxiliarycontrol provisions disclosed in Fig. 2 operates to reduce the departuresfrom the desired temperature, both in magnitude and frequency, and,therefore, more uniform working conditions will be maintained in thefurnace.

In Fig. 3 I have illustrated, more or less diagrammatically, amodification of the control arrangement disclosed in Fig. 1 whereinelectrical provisions are made for adjusting the control point orvarying the temperature of the furnace work chamber temperature. Inaddition, Fig. 3

- illustrates the use of my invention in a deflecsecondary winding 20which is in opposition to 'tive force produced by the thermocouple 4 hasdecreased to the value corresponding to the desired furnace worktemperature, the potential impressed on the galvanometer will have beenreduced to a value less than that required to maintain the galvanometerpointer 2 in engagement with the contact 9 or even intermediate thecontacts 9 and I0. Thus, the pointer 2 may deflect into engagement withthe contact H] to close an energizing circuit to the motor |'3 forproducing an opening adjustment of the fuel suptional type potentiometersystem. The galvanometer la if Fig. 3 may be generally like thegalvanometer of Fig. 1 but is preferably so constructed as to permitdeflection in one direction or the other from a mechanically zero orneutral position when an electromotive force of one polarity or theopposite is impressed across its terminals.

Specifically, in Fig. 3 a variable portion of an elongated potentiometerslidewire resistance 22, across which a suitable potential is adapted tobe maintained by a battery 23, is adapted to be inserted into theconductor 6 by adjusting the position of a slidewire engaging contact 24along the length of the slidewire 22. A rheostat 25 is provided inseries with the battery 23 for adjusting the potential drop across theslidewire resistance to a suitable value. As shown, the slidewirecontact 24 is carried by an internally threaded nut 26 which rides on ascrew threaded shaft 21. The

.screw threaded shaft 21 is supported by bearings 28 and 29 provided atopposite ends thereof and is adapted tobe rotated by manipulation of aknob 30 provided at the right end as seen in the drawings. An indicator3| is also carried by the nut 26 and is disposed in cooperative relationwith a suitably calibrated scale 32 for indicating the position to whichthe contact 24 is adjusted along the slide wire 22. i The contact 24 isalso maintained in engagement with a conductor 33 which is disposedclosely adjacent the slidewire resistance 22. Theconductor 33 isconnected by the conductor 6 to one terminal of the thermocouple 4, andthe right end of slidewire resistance 22 as seen in the drawings isconnected to one terminal of the galvanometer The polarity of battery 23is such as to produce. a potential drop across slidewire resistance 22which opposes the electromotive force produced by thermocouple 4.

In accordance with the arrangement of Fig. 3 the control point, or inother words the value of temperature maintained in the furnace 3, isadjusted by manipulation of the knob 30. The scale 32, therefore, maydesirably be calibrated in terms of temperature to be maintained in thefurnace 3.

vWhen the electromotive force generated by value in a manner similar tothat just described thermocouple 4 is substantially equal to thepotential drop produced across that portion of slidewire resistance 22between the right end thereof and contact 24, the current flow throughresistance 8 and galvanometer la will be substantially zero. Upondeparture of the temperature of the furnace work chamber from thedesired value after the said temperature has been stabilized at thedesired value for a considerable period, however, for example, upon anincrease in that temperature, the electromotive force produced by thethermocouple 4 will increase and as a result overbalance theelectromotive force derived from the slidewire resistance 22 and whichis opposed totween the resistance 8 and the galvanometer la immediatelybut instead is initially impressed in its entirety upon the galvanometeris because of the tendency of the capacitance l to prevent any suddenchanges in the potentials across its terminals. The consequentdeflection of the galvanometer pointer 2a into engagement with thecontact 9 energizes the motor l3 for rotation in the direction todecrease the supply of fuel to the furnace heating chamber.

Thecapacitance 1, as in the Fig. I arrangement, does not continueindefinitely to resist changes in potential across its terminals,however, but gradually charges until the electrometive force developedby the thermocouple 4 is divided between the resistance 8 and thegalvanometer ld in proportion to the relative resistances of theseparts. With no further change in the furnace work temperature thepotentials across the condenser l and galvanometer Ia will then bemaintained at these values. 7

When thereafter the furnace work chamber temperature begins to' returntoward the desired value, the electromotive force developed by thethermocouple 4 will begin to decrease to its original value. Thisdecrease in electromotive force is not immediately divided between theresistance 8 and the galvanometer id, but at first is assumed in full bythe galvanometer la because of the tendency of the condenser l to resistany change in potential across its terminals. The immediate result ofthis operation is that the deflection of the galvanameter pointer 2a, inresponse to the furnace temperature decrease, is accentuated.Consequently, prior to the time when the electromotive force of thethermocouple 4 has decreased to the value corresponding to the desiredfurnace work chamber temperature, the electromotive force-impressed onthe terminals of the galvanomater la will have been reduced to zero andeven reversed in polarity, the reversal in polarity being caused by theresidual electromotive force maintained across condenser l andresistance 8. The pointer 2a will, therefore, be moved out of engagementwith contact 9 and move into engagement with contact ill to therebyesnace work chamber temperature at the desired 75 for an increase infurnace work chamber temperature.

In Fig, 4 I have illustrated a modification of" the control systemdisclosed in Fig. lwherein an initially large corrective adjustment ofvalve i8 is first effected upon a change in the temperature in thefurnace 3, thereafter the initial magnification is eliminated, or morespecifically, the correction is reduced to a value which is proportionalto the furnace temperature departure, and thereafter additionalcorrective adjustments, commonly termed reset adjustments, are made ifthe furnace temperature has not returned to the desired value within apredetermined time depending upon the constants of the furnace and theload therein. The arrangement of Fig. 4 operates also to anticipate aneed for a fuel correction as in the arrangement of Fig. 1.

The additional control features attained in the arrangement of Fig. 4and not obtained in the arrangement of Fig. 1 are obtained by means of acontrol circuit 34 which is connected in parallel to the capacitance'land resistance 8. The control circuit 34 comprises a Wheatstone bridgenetwork 35, a resistance 36 and a capacitance 31. The Wheatstone bridgenetwork 35 includes resistance legs 38,39, 48 and 4| and is energized bya battery 42 through a rheostat 43 which is adjustable by means of aknob 44. The resistance legs 48 and 4i are desirably in the form of aslidewire resistance, as shown, and are engagedthe slidewire resistancefrom one end to'the other in accordancewith the adjustments of the fuelvalve [6 between its fully opened and fully closed positions.

The contact 45 is connected by means of a v conductor 46, in which thecapacitance 31 is connected, to the right end terminal of capacitance land resistance 8, as seen in Fig. 4, and the point of engagement 4'! ofresistance legs 38 and 39 is connected by a conductor 48, in which theresistance 36 is connected, to the left end terminal of capacitance Iand resistance 8. When the contact 45 is in engagement with the midpointof the slidewire resistance composed of resistance legs 48 and 4|, thepotential of the contact 45 is the same as that of the bridge point 41.Upon movement of the contact 45 in one direction or the other from thismidpoint on the slidewire resistance, however, a potential of onepolarity or the other is produced between the contact 45 and bridgepoint 41. The magnitude of this potential for a given movement of thecontact 45 along the slidewire resistance may be varied within limits byadjustment of the rheostat 43. Such a variation is known in the art asathrottling range adjustment.

The potential so derived between the contact 45 and ,bridge point 41 isimpressed upon the series circuit including resistance 36, capacitance land resistance 8 in parallel, and capacitance 31, and operates to causea charging and discharging current to flow into and out of thecapacitance 31 depending upon the polarity of the potential relativelyto the charge which may already be present upon the capacitance 31.After a. time interval depending upon the resistance of this seriescircuit and the capacity of the capacitance 31, the capacitance 31 willhave as great a charge on it that it canpossibly hold at the particularpotential value impressed upon it and as a result, the flow of chargingcurrent in the series circuit to the capacitance 31 will cease. Thiscondition, moreover, will prevail irrespective of the position ofjthecontact 45 along the slidewire resistance. It'is noted that the capacityof the capacitance 31 is large relative y to the capacity ofcapacitance 1. The capacity of capacitance 31 and the resistance of theseries circuit is adjusted so as to correspond to the temperature lagwithin the furnace 3. To facilitate. such adjustment the resistance 36and capacitance 31 may desirably be made adjustable. I

The operation of this embodiment of my' invention will now be described.Upon variation of the furnace work chamber temperature from the desiredvalue following stabilized operation of the control system with thecontact 45 in the position shown, for example, upon an increase infurnace temperature from the desired value, the electromotive forceproduced by the thermocouple 4 will increase, and accordingly. thegalvanometer pointer 2 will immediately deflect into engagement with thecontact 9, substantially the full change in thermoelectric electromotiveforce being initially impressed on the galvanometer l as in the Fig. larrangement. The motor I3 is then energized for rotation in thedirection to effect a closing adjustment of the fuel valve l6 andsimultaneously actuates the contact 45 to the left along the slidewireresistance as seen in the drawings. As thecapacitance 1 charges the newvalue of thermoelectric electromotive force divides between theresistance 3 and the galvanometer l-in proportion to their relativeresistances whereby the electromotive force applied to the galvanometerI is reduced somewhat. The value of electromotive force applied to thegalvanometer I, however, is ordinarily suflicient to maintainf thepointer 2 in engagement with contact 9 arid-therefore, if no otherelectromotive forces were impressed on the galvanometer circuit thepointer 2 would remain in engagement with the contact 9 until thetemperature within the furnacework chamber begins to return to thedesired value as in the Fig. 1 arrangement.

The adjustment of contact 45 to the left along the slidewireresistance,however, operates to impress an electromotive force on the seriescircuit referred to above which is of the proper polarity to cause acharging current to. flow through resistances 36 and I as required toincrease the potential drop across resistance f for the case underconsideration, namely a furnace temperature increase. This'chargingcurrent flows to the capacitance 31 and is effective to increase thepotential drop across resistance 8 at a rate determined by the capacityof capacitance 1. The

potential drop across resistance 8 and capaci tance 1 thus producedapproaches the value of electromotive force produced by the thermocouple4, and since these potentials are in opposition to each other, theelectromotive force applied to the galvanometer I decreases toward thevalue at which the contact 2 is intermediate the contacts 9 and i andwill even become less than this value as the potential drop acrossresistance 8 approaches that of the thermoelectric potential. Thiscauses the pointer 2 to separate from contact 9 and to move intoengagement with contact l0 whereby the motor I3 is energized forrotation in the direction to give an opening adjustment to the fuelvalve l and to actuate contact 45 diate the contacts 9 and Ill.

to the condenser 31. duced across resistance 3 by the charging currentto the right along the slidewire resistance. Such adjustment of thecontact 45 results in a gradual reduction in the potential drop acrossresistance 8, and accordingly, the electromotive force applied togalvanometer l gradually falls off to the value required to maintain thecontact 2 intermediate contacts 9 and Ill, and when that state isreached the pointer 2 moves out of engagement with contact Ill toward aposition interme- This causes deenergization of motor l3 for rotation.

Thus, the immediate effect of an increase in the furnace work chambertemperature from the desired value is an initially large closingadjustment of the fuel valve l6 followed thereafter by an openingadjustment of smaller magnitude than the closing adjustment. If thefurnace work chamber temperature has then been restored to the desiredvalue, the galvanometer i will remain in the position with contact 2intermediate contacts 9 and Ill and the control system will bestabilized.

If the furnace work chamber temperature has not been restored to thedesired value at this time, but starts to return and approaches thatvalue befbre the flow of charging current to the condenser 31 ceases toflow, the electromotive force produced by the thermocouple 4 will beginto decrease to its original value. The full reduction in thethermoelectric electromotive force will be initially applied to thegalvanometer I because of the action of condenser 1, and as a re sult,the galvanometer pointer 2 will be deflected into engagement withcontact 10 to energize the motor 13 for operation in the direction toeffect an opening adjustment of the fuel valve IS in anticipation of theneed for such a correction as in the arrangement of Fig. 1. The motor l3will'siinultaneously actuate the contact 45 to the right along theslidewire resistance, and thus eflect a reduction in the flow ofcharging current The potential drop proflow therethrough will then bereduced at a rate depending upon the capacity of capacitance 1 which, asnoted -hereinbefore, tends to maintain the potential value existingthereon at any instant. It is noted that depending upon the extent ofthe adjustment of contact 45 along the slidewire resistance that acharging current may even be established through the resistance 3 in thereverse direction as a result of the capacitance 31 discharging to causea further reduction in the potential drop across resistance 8.

The reduction in potential drop thus produced across the resistance 3assists the reduction in potential drop produced thereacross as a resultof the condenser 1 and resistance 8 finally assuming its share of thedecrease in thermoelectric electromotive force and operates to cause thegalvanometer pointer 2 to return to a. position between the contacts 9and ID at substantially the same time that the thermoelectricelectromotive returns to its original value corresponding to the desiredfurnace work chamber temperaure.

In the case wherein the furnace work chamber temperature does not returnto the desired value within a predetermined time, depending upon thecapacity of capacitance 31 and the resistance oi the series circuitincluding the bridge network 35 and resistances 8 and 36, the charge onthe capacitance 31 approaches the maximum value which the capacitance 31can hold for the particular value of applied electromotive force and as|3 to effect an additional fuel valve closing adjustment, and anadditional adjustment of contact 45 toward the left along-the slidewireresistance. causes a further flow of charging current through theresistance 8 to the capacitance 31 and thereby operates to effect areturn movement of the galvanometer pointer 2 to a position between thecontacts 9 and ID, and accordingly, to deenergize the motor |3 forrotation. 'Such additional fuel valve correcting adjustments andadjustments of the contact 45 along the slidewire resistance areproduced until the fuel valve l6 and contact 45 have been adjusted totheir extreme positions or until the temperature within the furnace workchamber has been reduced to the desired value.

In Fig. I have illustrated a modification of the control arrangementdisclosed in Fig. 4. The control system of Fig. 5 includes a Wheatstonebridge network 35, a resistance 36'and a capacitance 31 all of'which maybe identical to the correspondingly identified parts of Fig. 4. In

Fig. 5 the bridge network 35, resistance 36 and.

capacitance 3'! are connected in a series circuit across the terminalsof the galvanometer instead of across the capacitance 1 and resistance 8as in Fig. 4. A resistance 49 which is adjustable by means of a knob 50is included in this series circuit. parallel with the galvanometer i andthe resistance 49.

With this modification of my invention, when the furnace work chambertemperature has been stabilized at the desired value, the pointer 2 ofthe galvanometer i will be disposed between the contacts 9 and it) outof engagement with both, and accordingly, the motor 3 will bedeenergized. Upon variation in the furnace chamber from the desiredvalue, for example, upon an increase in temperature the electromotiveforce developed by the thermocouple 4 will increase and substantiallythe full change in electromotive force will initially be impressed uponthe terminals of the galvanometer by virtue of the action of thecondenser l. The galvanometer I will then deflect the pointer 2 intoengagement with the contact 9 to effect operation of the motor |3in thedirection to cause a closing adjustment of the fuel valve i6. Initialmagnification in the adjustment of the fuel valve IS in this arrangementis effected as a result of the operation of the resistance 49 and thecondenser 5|. It is noted that the increased electromotive forceimpressed on the galvanometer l as a result of the increasedthermocouple electromotive force causes a flow of charging currentthrough the resistance 49 into the condenser 5|. When, subsequently thecondenser 1 begins to assume its proper proportion of the electromotiveforce developed by the thermocouple 4the potential drop across thegalvanometer I will tend to decrease but when this happens the condenser5| begins to discharge through the resistance 49 and the galvanometerThis action tends to maintain the galvanometer with the pointer Tin itsdeflected position in engagement with the contact 9. The deflection ofthe pointer 2 into engagement with the contact 9 therefore is prolongedand as a This adjustment of the contact 45' A capacitance 5| isconnected in This adjustment of the contact $5 for the case underconsideration is toward the right and results in the application to thecondenser 5| of a potential of the proper polarity to cause thegalvanometer to deflect the pointer 2 out of engagement with the contact9 and into engagement with the contact In. The motor I3 is thenenergized for rotation in the opposite direction to effect 'a partialclosing adjustment of the fuel valve and a partial return of the contact45 towards its original position. This action continues until thepotential impressed 0n the condenser 5| is the correct value to maintainthe galvanometer pointer 2 between the contacts 9 and i0.

As long the furnace temperature is away from the desired control point,however,- the control system is not stable because of the action of thecondenser 31. The potential difference between the contact 45 and thebridge point 4! is divided between the condenser 5| and the condenser31, the potential across the condenser 5| being determined mainly by thepotential drop across the galvanometer I. The difference between thatpotential drop and that betweenthe contact and the bridge point 41 isultimately assumed by the condenser 31. When the condenser 31 hascharged to its final potential, the potential across the condenser 5|will have increased. to that potential which would be maintained acrossthe galvanometer I if the circuit including resistance 49 and condenser5| connected in parallel thereto were disconnected. This potential againcauses the galvanometer to deflect the pointer 2 into engagement withthe contact 9 and thereby effects energization of the motor I3 forrotation in the proper direction to effect an additional fuel valveclosing adjustment. The resetting adjustments of the control system ofFig. 5 are effected in this manner, the capacitance of the condenser 31and the resistance of the resistance 36' being assigned valuescorresponding to thetemperature lag encountered in the furnace 3.

As the furnace temperature begins to return to the desired value theelectromotive force developed by the thermocouple 4 decreases andbecause of the action of the condenser l th full effect of thisdecreased electromotive force is immediately impressed on thegalvanometer I. This causes the galvanometer to deflect into engagementwith the contact H! to effect energization of the motor I3 in thedirection to cause a fuel valve opening adjustment. Such fuel valveopening adjustment is effected prior to the return of the furnacetemperature to the desired value and therefore in anticipation of theneed for such correction. In addition the control system operates in themanner described for case of a temperature decrease to effect an initialmagnification in such fuel valve opening adjustment.

The overall effect of such operation is that the furnace temperature isquickly returned to the desired value upon deviation therefrom.Overgalvanometer.

ment for effecting the desired corrective adjustments of the fuel valveI8 in response to deflections of the sensitive element'of thegalvanometer. It will be understood that the arrangement disclosed inFigs. 6 and 7 maybe utilized in connection with each of the controlcircuit arrangements disclosed in Figs. l-5, if desired.

The control circuit arrangement shown in Fig. 6 is of the deflectionalpotentiometer type described in connection with Fig. 3 and its operationis the same as the control circuit arrangement of Fig. 3. In Fig. 6 thegalvanometer is of the mirror type and has been designated by threference character II). The sensitive element of the galvanometer lbcarries a mirror Ic which deflects in accordance with the electromotiveforce impressed upon the terminals of the This also includes arelatively stationary source of light or lamp 52, a pair of photocells53 and 54 which, as shown, may be housed within the same envelope andare connected to the terminals of an electronic amplifier 55. A lens 55positioned between the lamp 52 and the galvanometer mirror I0. is alsoprovided for focussi'ng the reflected beam of light from the mirror Icon the photocells. I

When the furnace workchamber temperature is at the desired value and thecontrol circuit arrangement is stabilized the mirror Ic of thegalvanometer will be in its normal neutral position and the beam oflight reflected by the mirror Ic will then shine equally on bothphotocells 53 and 54. When the galvanometer deflects in one direction,more light is reflected on one photocell 53 or 54 than on the other andupon reflection of the galvanometer in'the opposite direction more lightis reflected on the other photocell. The current passed by thephotocells is amplified by the electronic amplifier 55 and the latteropcrates when one photocell receives more light than the other toselectively control the energization of a reversible electrical motor 51for rotation in one direction or the other. The reversible electricalmotor 51 is of the rotating field induction type and includes a winding58 which is continuously energized from'the alternating current supplylines L and I. through a condenser 58, and also includes a pair ofoppositely wound windings 68 and GI which are adapted to be selectivelyenergized by the amplifier 55 for controlling the direction of rotationof the motor.

One form of electronic amplifier 55 which may desirably be employed inthe arrangement of Fig. 6 is disclosed in Fig. '1 and, as shown,includes electronic valves 82, 83 and 54. The electronic valve 62 is atwin triode and the electronic valves 68 and 64 ar tetrodes.

ode 61 and a heater filament 68, and the other triode includes an anode59, a control grid 18,

a cathode 1| and a heater filament 12. The

the low voltage secondary winding 88 of a combination step-up andstep-down transformer 84 having a primary winding 85 and additionalsecondary windings 86, 81 and 88. The heater filaments 58 and 12 maydesirably be connected in parallel to the transformer secondary winding88.

alternative arrangement One triode of the valve .82 includes an anode85, a control grid 56, a cathof winding 88.

Energizing current is supplied the heater filaments 11 and 82 o! thetetrodes 58 and 84, respectively, from the transformer secondary winding85. The heater filaments 11 and 82 may desirably be connected inparallel to the winding 85.

Anode voltage is supplied the electronic valve 82 iromthe transformersecondary winding 81. The anode circuit of the triode including theanode 55 may be traced from the upper end of winding 81 through aconductor 88 to a resistance 88, anode 85, cathode 81, a biasingresistance 8| and a conductor 82 to the lower end of winding 81. Anodevoltage is supplied the triode including the anode 88 through a circuitwhich may be traced from the upper end of winding 81 to conductor 88 toa resistance 88, anode 58, cathode 1I, biasing resistance 8| andconductor 82 to the lower end of winding". As shown, a condenser 84 isconnected between the anodes 85 and 88 of valve 52.

Anode voltage is supplied the tetrodes 58 and 64 from the transformersecondary windings 81 and 88 through a circuit including the opposedmotor windings 58 and 5|. Specifically, the anode circuit of tetrode 88may be traced from the lower end of winding 88 through a conductor 85 towinding 58 of motor 5L anode 18, cathode 18, a biasing resistance 88,conductor to the upper end of winding 88. The anode circuit of tetrode84 may be traced from the.

lower end of winding 88 through conductor 85 to motor winding 8i, anode18, cathode 8|, biasing resistance 85, conductor 88 and the transformersecondary wlnding'81 to the upper end As shown the screen electrodes 14and 19 of the tetrodes 58 and 54 respectively are connected by aconductor 81 to the point of connection of the transformer secondarywindings 81 and 88. The input circuit of the tetrode 58 is controlled inaccordance with the conductivity of the triode including the anode 88and to this end the control electrode 15 is connected by a conductor 88to the anode 58. Similarly, the input circuit of the tetrode 54 iscontrolled in accordance with the conductivity of the triode includingthe anode 85, the control electrode 88 being connected to the anode 55by means of a conductor 88.

The input circuits of the triodes contained in the electronic valve 82are controlled in accordance with the conductivity of the photoelectriccells 58 and 54 and thereby in accordance with the extent to which thelatter are illuminated.

The photoelectric cell 58 is energized by a portion of the transformersecondary winding 81 thrd'ugh a circuit which may be traced from a tapI88 on the winding 81 to a conductor III, the anode of photocell 58, thecathode thereof. a resistance I82 and the conductor 82 to the lower endof the winding 81. The photocell 54 is energized through a circuit whichmay be traced from the tap I88 on the winding 81 through c onductor illto the anode of photocell 54, the cathode thereof, a resistance I88 andthe conductor 82 to the lower end of the winding 81. The point ofengagement of the resistance I82 and the cathode of the photocell 58 isconnected by a conductor I84 to the control electrode 45 and the pointof engagement of the resistance I88 and the cathode oi the photocell 54is connected-by the conductor I55 to the control electrode 18.

When both photocells 58 and 54 are equal y conductive the potentialimpressed on the conin the conductivity of the tetrode 63.

trol electrode 66 will be the same as that impressed on the controlelectrode 1.0 and consequently the potential impressed on the controlelectrode 15 of valve 63 will be the same as the potential impressed onthe control electrode 80 of the valve 64. Current of substantially thesame magnitude will then flow in both of the motor windings 60 and GIand accordingly the motor will not be energized for rotation in eitherdirection but will remain stationary.

When the photocell 53 is illuminated to a greater extent than thephotocell 54, however, the current flow through the resistance I02 willbe greater than that through the resistance I03 and consequently thepotential impressed on the control electrode 66 will be rendered lessnegative than that impressed on the control electrode 10. This willcause the triode including the anode 65 to become more conductive thanthe other triode, and accordingly, the potential drop across theresistance 90 is increased relatively to that across the resistance 93.The control electrode '80 is then rendered less negative with respect tothe potential of the cathode 8| and as a result the current flow throughthe motor winding 6! is increased. At the same time the current flowthrough the motor winding 60 is decreased because the illumination ofthe phovtocell 54' is decreased when the illumination of the photocell53 is increased. Thus, the potential of the control electrode 10 isrendered more negative with respect to the potential of the cathode Hwhereupon the potential of the control electrode is rendered morenegative with respect to the cathode 16 to eiTeot a reduction With thecurrent flow through the motor winding 6| thus increased relatively tothe current flow through the motor winding 60 the motor 51 will beenergizeol for rotation in one direction or the other. Similarly, whenthe photocell 54 is illuminated to a greater extent than the photocell53 the current flow'through the motor winding 60 will be increasedrelatively to that through the motor winding 6! whereupon the motor 51will be energized for rotation in the opposite direction.

While in the drawings and the foregoing description I have disclosed theuse of the present invention in connection with thermocouple measuringsystems, it will be understood that the" invention is not to beconstrued as being limited to such use but if desired may be employedwith other type measuring systems which are adapted to produce avariation in a direct current electromotive force upon change in themagnitude of a condition it is desired to control. For example, thepresent invention may advantageously be utilized in connection withWheatstone bridge circuits. In such arrangements a temperatureresponsive resistance which is subjected to the temperature conditionunder control is ordinarily provided in one arm of the bridge circuitand operates to control the state of balance of the bridge circuit inaccordance with the magnitude and the changes in magnitude of thetemperature condition to thereby produce an unbalanced electromotiveforce of one polarity or of the opposite polarity between the bridgecircut output terminals. It is contemplated that this unbalanced directcurrent electromotive force may be connected to the conductors 5 and 6of Figs. 1 6 in lieu of the thermocouple I for controlling the conditionby means of the apparatus of the-present invention.

While in accordance with the provisions of the statutes, I haveillustrated and described the best form of myinvention now known to me,it will be apparent to those skilled in the art that changes may be madein the form of the apparatus disclosed without departing from the spiritof my invention as set forth in the appended claims, and that in somecases certain features of my invention may sometimes be used toadvantage without 'a corresponding use of other features.

Having now described my invention, what I claim as new and desire tosecure by Letters Patent:

1. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to produce an electromotiveforcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, meansresponsive to the defiections of said elementto regulatev said condition, and auxiliary means to modify the effect ofvariations of the electromotive force produced by said first mentionedmeans on said device in accordance with the trend of the variations insaid condition to anticipate the need for regulation of said condition.

2. In a control system, a device having an element which is defiectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsiveto the defiections of said elementto regulate said condition, and physically stationary means associatedwith said device to modify the effect of variations of the electromotiveforce produced by said first mentioned means on said device inaccordance with the trend of the variations in said condition toanticipate the need for regulation of said condition.

3. In a control system, a device having an element which is defiectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, and electrical reactance andresistance means associated with said device to modify the eifect ofvariations of the electromotive force produced by said first mentionedmeans on said device in accordance with the trend of the variations insaid condition to anticipate the need for regulation of said condition.

4. In a control system, a device having an element which isdefiectable'from a normal, neutral position, a thermocouple adapted toproduce an electromotive force which is variable in accordance with thechanges in a variable condition from a predetermined value. connectionsto impress said electromotive force on said device, means responsive tothe deflections of said element to regulate said condition, andelectrical reactance and resistance means connected in circuit with saidthermocouple and said device to modify the effect of variations of theelectromotive force produced by said thermocouple on said device inaccordance with the trend of the variations in said condition toanticipate the need for regulation of said condition.

5. In a control system, a galvanometerhaving an element which isdeflectable from a normal neutral position, a thermocouple adapted toproduce an electromotive force which is variable in accordance with thechanges in a variable condition from a predetermined value, connectionsto impress said electromotive force on said galvanometer, meansresponsive to the deflections ance with the changes in a variablecondition from a predetermined value, connections to impress saidelectromot-ive force on said device, means responsive to the deflectionsof said element to regulate said condition, and electrical capacitanceand resistance means connected in circuit with said thermocouple andsaid device to modify the effect of variations of the electromotiveforce produced by said thermocouple on said device in accordance withthe trend of the variations in said condition to anticipate the need forregulation of said condition.

- 7. In a control system, a device having an element which isdefiectable from a normal, neutral position, a thermocouple adapted toproduce an electromotive force which is variable in accordance with thechanges in a variable condition from a predetermined value, connectionsto impress said electromotive force on said device, means responsive tothe deflections of said element to regulate said condition, andelectrical inductance and resistance means connected in circuit withsaid thermocouple and said device to modify the effect of variations ofthe electromotive force produced by said thermocouple on said device inaccordance with the trend of the variations in said condition toanticipate the need for regulation of said condition.

8. In a control system, a galvanometer having an element which isdefiectable from a normal. neutral position, a thermocouple disposed ina region the temperature of which it is desired to maintain at apredetermined value, connections to impress the electromotive forceproduced by said thermocouple on said galvanometer, means responsive tothedeflections of said element to regulate the supply of heating mediumto the region in which said thermocouple is located, and auxiliary meansto modify the effect of variations of the electromotive force producedby said thermocouple on said galvanometer in accordance with the trendof the temperature changes in said region to anticipate the need forcorrection in the supply of heating medium to said region.

9. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to prod'uce an electromotiveforce which is variable in accordance with the changes in a variablecondition from a predetermined value, connections to impress saidelectromotive force on said device, an adjustable source ofelectromotive force connected in circuit'with said device and said meansand opposed to said first mentioned electromotive force, means to adjustsaid adjustable source of electromotive force to vary the magnitude ofthe electromotive force opposed to said first mentioned electromotiveforce, means responsive to the deflections of said element to regulatesaid condition, and auxiliary means to modify the effect of variationsof the electromotive force produced by said first mentioned means onsaid device in accordance with the trend of the variations in saidcondition to anticipate the need for regulation of said condition.

10. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means-continuously out of physical contact withsaid element but responsive to the deflections thereof to regulate saidcondition, and auxiliary means to modify the eilect of variations of theelectromotive force produced by said first mentioned means on saiddevice in accordance with the trend of the variations in said conditionto anticipate the need for regulation of said condition.

11. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, auxiliary means to modify the efiectof variations of the electromotive force produced by said firstmentioned means on said device in accordance with the trend of thevariations in said condition to anticipate the need for regulation ofsaid condition, and follow-up means controlled by said responsive meansto neutralize the effect on said device of variations in saidelectromotive force.

12. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, auxiliary means to modify the eflectof variations of the electromotive force produced by said firstmentioned means on said device in accordance with the trend of thevariations in said condition to anticipate the need for regulation ofsaid condition, and follow-up means adapted to be adjusted by saidresponsive means to neutralize the effect on said device of variationsin said electromotive force including electrical bridge circuit meansadapted to have an unbalanced electromotive force produced therein inaccordance with the adjustment of said follow-up means and means tocontrol said device by said unbalanced electromotive force.

13. In a control system, a device having an element which is deflectablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, auxiliary means to modify the eflectof variations of the electromotive force produced by said firstmentioned means on said device in accordance with the trend of thevariations in said condition to anticipate'the need for regulation ofsaid condition, and follow-up means adapted to be adjustedby saidresponsive means to neutralize the effect on said device-of variationsin said electromotive force including electrical bridge circuit meansadapted to have an unbalanced electromotive force produced therein inaccordance-with the adjustment of said follow-up means and connectionsto impress said unbalanced electromotive force on said device.

14. In a control system, a device having'an element which isdeii'ectable from a normal, neutral position, means to produce anelectromotive force which is variable in accordance with the changes ina variable condition from a predetermined value, connections to impresssaid electromotive force on said device, meansresponsive to thedeflections of said element to regulate said condition, auxiliary meansto modify the effect of variations of the electromotive force producedby said first mentioned means on said device in accordance with thetrend of the variations in said condition to anticipate the need forregulation of said condition, follow-up means controlled force which isvariable in accordance with the changes in a variable condition from apredetermined value, connections to impress said electromotive force onsaid device, means responsive to the deflections of said element toregulate said condition, auxiliary means to modify the effect 01'variations of the electromotive force produced by said first mentionedmeans on said device in accordance with the-trend of the variations insaid condition to anticipate the need for regulation of said condition,follow-up means adapted to be adjusted by said responsive means toneutralize the effect on said device of variations in said electromotiveforce including electrical bridge circuit means adapted to have anunbalanced electromotive force produced therein in accordance with theadjustment of said followup means and connections to impress saidunbalanced electromotive force on said device, and reset meansassociated with said follow-up means to dissipate the neutralizingefl'ect of said followup means on said device.

16. In a control system, a device having an element which'is defleotablefrom a normal, neutral position, means to produce an electromotive forcewhich is variable in accordancewith the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, auxiliary means to modify the eiiectof variations of the electromotive force produced by said firstmentioned means on said device in accordance with the trend of thevariations in said condition to anticipate the need for regulation ofsaid condition, follow-up means adapted to be adjusted by saidresponsive means to neutralize the effect on said device of variationsin said electromotive force including electrical bridge circuit meansadapted to have an unbalanced electromotive force produced therein inaccordance with the adjustment of said followup means and connections toimpress said unbalanced electromotive force on said device, and

, reset means associated with said follow-up means to dissipate theneutralizing effect of said followup means on said device, said resetmeans including electrical reactance included in said second mentionedconnections.

17. In a control system, a device having an element which is defiectablefrom a normal, neutral position, means to produce an electromotive iorcewhich is variable in accordance with the changes in a variable conditionfrom a predetermined value, connections to impress said electromotiveforce on said device, means responsive to the deflections of saidelement to regulate said condition, auxiliary means to modify the efiectof variations of the electromotive force produced by said firstmentioned means on said device in accordance with the trend of thevariations in said condition to anticipate the need for regulation ofsaid condition, followup means adapted to be adjusted by said responsivemeans to neutralize the efi'ect on said device of variations in saidelectromotive force including electrical bridge circuit means adapted tohave an unbalanced electromotive force produced therein in accordancewith the adjustment of said follow-up means and connections to impresssaid unbalanced electromotive force on said device, and reset meansassociated with said follow-up means to dissipate the neutralizingefiect of said follow-up means on said device,

said reset means including electrical capacitance and resistanceincluded in said second mentioned connections. 7

18. In a control system, a device actuable from a normal, neutralcondition of operation, means to produce an electromotive force which isvariable in accordance with the changes in a variable condition from apredetermined value, connections to impress said electromotive force onsaid device to actuate said device from said normal, neutral conditionof operation, means responsive to changes in the condition of operationof said device to regulate said condition, and physically stationarymeans associated with said device to modify the eifect of variations ofthe electromotive force produced by said first mentioned means on saiddevice in accordance with the trend of the variations in said conditionto anticipate the need for regulation of said con- 'dition.

19. In a control system, a device actuable from a' normal, neutralcondition of operation, a

thermocouple adapted to produce an e.ectromotive force which is variablein accordance with the changes in a variable condition from apredetermined value, connections to impress said electromotive force onsaid device to actuate said device from said normal, neutral conditionof operation, means responsive to changes in the condition of operationof said device to regulate said condition, and electrical reactance andresistance means connected in circuit with said thermocouple and saiddevice to modify the effect of variations oi" the electromotive forceproduced by said thermocouple on said device in accordance with thetrend of the variations in said condition to anticipate the need forregulation of said condition.

THOMAS R. HARRISON,

